Over the last few decades, scientific studies resulted in many discoveries in the field of electronics pertaining to the application of new materials. Nitrides of aluminium, gallium and indium are an especially attractive group of chemical compounds to be used in new electronic technologies. In the processes of synthesis of the said nitrides, ammonia with particularly high purity—less than 0.1 ppm of impurities—is used. On the other hand, a need arises for purification of the syngas (hydrogen and nitrogen) stream in ammonia synthesis, in which catalysts with higher efficiency than that of the conventional iron catalyst are used. Such catalysts are much more sensitive to impurities present in the syngas stream.
Purity of ammonia is connected both with purity of the syngas used for production of ammonia and with methods for purification of raw ammonia.
Methods for obtaining a syngas with proper purity (mixture of H2 and N2) are known and described in many sources of literature [W. Bobrownicki, S. Pawlikowski, “Technologia zwiazków azotowych”, WNT, Warsaw 1974; Information materials of Kellogg Brown & Root, http://www.kbr.com, dated May 15, 2012]. Final purification of the fresh gas from water vapour and carbon oxides is carried out by adsorption on molecular sieves or washing of the gas with a stream of liquid ammonia or liquid nitrogen. The purity of these gas streams is sufficient to obtain technical ammonia on a large commercial scale, but completely unsatisfactory for application of the obtained NH3 in electronics. For this type of application, it is necessary to remove such impurities as H2O(g), COx, CH4, O2 and Ar from ammonia.
In order to purify ammonia to high purity, two basic methods are used. The older one consists in passing gaseous ammonia containing 80 ppm of impurities under atmospheric pressure through liquid ammonia with dissolved metallic sodium. After purification, NH3 contains 0.6 ppm of impurities in the form of oxygen-containing compounds [U.S. Pat. No. 4,075,306]. The other method for obtaining high-purity ammonia is fractional distillation of liquid ammonia under a pressure of 2-30 MPa. Ammonia with 99.99% purity was purified to a level of 10 ppm of impurities [U.S. Pat. No. 7,001,490]. of liquid ammonia may be preceded by stages of hydrocarbons and water removal by adsorption. The adsorption process is carried out using a known bed, e.g. granulated activated carbon for removal of hydrocarbons and calcium sulfate(VI) for removal of water. Such a process is known from the patent description U.S. Pat. No. 7,297,181, according to which ammonia with a purity of 99.9995% has been obtained.
Use of metallic sodium in the first method practically precludes its application in the field of electronics, because sodium is an element considered exceptionally inadvisable in semiconductor materials. In the next two methods, a process of distillation is used, requiring complex equipment and using a significant amount of energy.
The goal of the invention was to provide a method which allows for obtaining high-purity ammonia, technologically convenient on a large scale, and enables efficient purification of both syngas and impure ammonia.